1. Field of the Invention
This invention relates to a suspension system for a steered wheel of a vehicle and more particularly to an independent front suspension using S-cam brakes with improved steering radius and load capacity while maintaining good handling characteristics.
2. Description of the Related Art
A variety of suspension systems are available for cars, trucks, and other wheeled vehicles. The particular suspension design selected for a particular vehicle depends on a number of considerations. These considerations include the purpose of the vehicle, the gross vehicle weight, whether the suspension supports the front or the rear of the vehicle, whether the wheels are steerable and whether the wheels are driven. No suspension system is ideal for all applications.
For heavy-duty applications, a conventional beam axle design provides strength, rigidity, accurate steering and tire-wear control. However, the beam axle translates a singular tire input (bump) to the other side wheel, thereby affecting steering performance parameters to the vehicle. Independent wheel suspensions isolate the right and left side wheel inputs.
One important consideration in independent suspension design is the maximum steering angle. A greater steering angle affords a tighter radius of turn and hence, is preferable in order to increase vehicle maneuverability. In the United States S-cam type brakes are typically used on heavy-duty truck and bus wheels. These brakes have a camshaft assembly, slack adjuster, and brake actuator assembly that are all mounted on the wheels and thus turn together with the wheel during steering. These components present a challenge for the design of a suspension in a relatively small space and at the same time with a small turning radius for the suspension. Typically, these components require a relatively wide space in the suspension to prevent interference between these components and the suspension support elements during turning of the vehicle. However, increasing the spacing from the wheel to the suspension results in increasing the scrub radius of the suspension.
The scrub radius is the distance, at the ground, between a vertical line passing through the center of the vehicle tire and the projection of the axis of rotation of the wheel when viewed from the front of the vehicle. In essence, the scrub radius defines the moment arm for road surface induced forces that apply a moment to the suspension. However, some scrub radius is required for directional stability and straight line performance. The greater the scrub radius, the greater will be the moment applied to the suspension. As the magnitude of the moment increases, more resistance is in the form of larger air springs or stronger suspension/steering components, for example, is required. Further, with larger scrub radii, the handling and maneuverability of the suspension declines substantially Further, larger and heavier parts are required to handle the increased resistance requirements. Thus, it is desirable to keep the scrub radius as small as possible without negatively impacting stability and performance. However, minimizing the scrub radius militates against providing a smaller turning radius for the suspension for S-cam brake suspensions. Thus, suspensions for S-cam brakes have heretofore been a compromise between weight, maneuverability, steering radius and load capacity. No one suspension has been able to maximize these suspension requirements for S-cam brakes in heavy-duty suspensions.
There is a need for heavy-duty independent front suspensions with S-cam brakes having smaller steering angles without sacrificing other suspension qualities such as load capacity, weight and handling.